(1) Study of E. coli alkaline phosphatase reveals a possible regulatory role for negative cooperativity. It provides a means for a rapid surge or decrease in enzymic activity through changes in the concentration of an allosteric effector such as Mg(II) which can practically desensitize the negative cooperativity. (2) Mechanistic study of 2-aza-epsilon-adenylylated glutamine synthetase (GS) reveals the catalytic cycle for the adenylylated GS. Topographical information on the adenylylation and catalytic sites and substrate induced conformational changes of the adenylylated enzyme were obtained using a spin-labeled Tempo-adenylylated GS. Results from fluorescence and polarization studies on the binding of L-methionine-S-sulfoximine and its R-isomer to the Mg(II) activated unadenylylated GS confirm the homologous subunit interaction in GS. (3) Mechanistic study on the activation of cyclic nucleotide phosphodiesterase by calmodulin may reveal a general mechanism for calmodulin activation of enzymic activity. (4) Theoretical analysis of cyclic cascade model and the study of adenylylation-deadenylylation of the GS system and phosphorylation-dephosphorylation of protein are being continued. The mechanism and regulation of actomycin ATPase were investigated.